Cornelius keg

The soda is referred to as "premix" in the industry, as compared to "postmix" bag-in-box (BiB) packages which are concentrated syrup.

Cornelius kegs are now widely used for homebrewed beer and other homemade beverages such as soda or nitro cold brew coffee.

A Cornelius keg is a stainless steel cylinder typically rated for a maximum pressure of 130 pounds per square inch (9.0 bar).

There are three openings in the keg: a large central hole for cleaning and filling, and two ports for pressurizing and dispensing.

The central opening is used for filling and cleaning the keg and is large enough to permit reaching inside for hand scrubbing.

The lid also provides a pressure relief valve that is typically identified by a circular pull-ring (like a key ring).

Compared to pin locks, this is not as easy to visually distinguish, so additional visual cues are sometimes provided: the gas and liquid posts may use different colored rubber gaskets, the gas post may have small notches to distinguish it, and the kegs themselves may label the ports as "IN" and "OUT" or may have a bump to mark one of the ports.

This design is ideal for soda, beer, and other carbonated beverages which must be stored under pressure to keep the gas dissolved in the liquid.

Sodas are carbonated up to 5 volumes of CO2, which requires a pressure of 38.9 pounds per square inch (2.68 bar) at a serving temperature of 40 °F (4 °C).

Surplus Cornelius kegs, which are largely obsolete from the soft-drink industry, have been adopted by homebrewers as an efficient alternative to bottling.